Question regarding cache drive(s)

[tbonedude420]

Hey all!

 

I've currently got a 10 disk, 70 TB array, and a 500gb nvme for cache.

 

The question,

Would I be better off upgrading to a 1tb single drive nvme, or adding in a second 500?

In theory there could be more IOPS with two drives, but im not quite sure. 

Speed isnt really a concern seeing as its NVME.

 

I also have 2x250 gb nvme's with adapters laying around.

 

What would you do?

Double up, and get a second five hundo

Swap out for a 1tb.

Add-on 2 more 250's and compare performance?

(This is an option since im not using my pci slots for anything else at the moment)

I have either 4 or 5 pcie slots, 1 for a 9211-8i raid card, one for the cache drive, have at least 2 more spots open to use.

 

Media programs transcode in ram, but the library information, poster art, and a single w10VM all live in cache land.

 

I can provide as much data as needed. Basic specs are xeon e5 2670v1 (two), ASRock EP2C602-4L/D16, unraid 6.8.2

[testdasi]

Use your existing 2x250GB to separate write-heavy and read-heavy data.

Something like this:

• Set all shares with Cache = Yes to Cache = No. You don't have parity so there's no need for write cache (even if you do, I would turn on Turbo Write rather than wasting SSD write cycles as a wriet cache).
• Set the 2x250GB in a RAID1 cache pool
• Mount the 500GB as UD and use the console to move data over (except any temp data).
• Then use the 500GB as temp drive for write-heavy activities.
  • I doubt you will see a diff in performance but if you have a VM that needs a really fast vdisk, just put the vdisk in the 500GB.

Alternatively, if let's say you want the fastest possible storage performance for your VM, you can set 1x250GB in cache and 1x250GB as UD as temp drive for write-heavy activities. Then pass through the 500GB to your VM as a PCIe device i.e. stub it and select it in Other PCIe device section of the VM GUI.

 

 

 

[tbonedude420]

So, hmm... choices to make...

 

I thank you for the reminder of Unassigned Devices. I had checked it out once, but then forgot about it.

 

I am curious as to what kind of performance gains could be had in a 2x250 cache array, but my understanding is it would be 384gb?

I would very much be interested in passing a 250 directly to a VM, thats an idea worth some exploration I think.

 

I think I will do some testing, and report back here hopefully with geeky pics or something!

 

Many thanks for the response and reminder on UD, man what a good plugin how could I forget?!

 

A side note, for passthrough stuff, I need to enable IOMMU stuff or something? I may have to refer to some spaceinvader one videos in my near future.

I also toyed with a plain jane sata ssd before and used that as write heavy cache space, and I killed it. (Not entirely, a full long format later, and a update to the firmware and shes back up to mostly full speed again) but not something im quick to return back to anytime soon. the 12tb seems to handle its own as the 'main drive'. given the size gap difference, it tends to be the first thing hit for incoming data / downloads / ect.